President Donald Trump has attacked a top union leader on the annual US holiday that celebrates workers.

Mr Trump lashed out on Twitter following criticism from the president of the American Federation of Labour and Congress of Industrial Organisations (AFL-CIO) Richard Trumka.

Mr Trump tweeted on Labour Day that Mr Trumka “represented his union poorly on television this weekend”.

He added: “it is easy to see why unions are doing so poorly. A Dem!”

The president’s attack came after Mr Trumka appeared on Fox News Sunday over the weekend where he said efforts to overhaul the North American Free Trade Agreement (Nafta) should include Canada.

Mr Trumka, whose organisation is an umbrella group for most unions, said the economies of the United States, Canada and Mexico are “integrated” and “it’s pretty hard to see how that would work without having Canada in the deal”.

Happy Labor Day! Our country is doing better than ever before with unemployment setting record lows. The U.S. has tremendous upside potential as we go about fixing some of the worst Trade Deals ever made by any country in the world. Big progress being made!

Mr Trump had previously said on Twitter that there was “no political necessity” to keep Canada in Nafta.

But it is questionable whether Mr Trump can unilaterally exclude Canada from a deal to replace the three-nation Nafta agreement, without the approval of the US Congress. Any such move would likely face lengthy legal and congressional challenges.

The Worker in America is doing better than ever before. Celebrate Labor Day!

Trump administration negotiations to keep Canada in the re-imagined trade bloc are to resume this week as Washington and Ottawa try to break a deadlock over issues such as Canada’s dairy market and US efforts to shield drug companies from generic competition.

Mr Trump wants to get a trade deal finalised by December 1.

Mr Trumka also said of Mr Trump: “The things that he’s done to hurt workers outpace what he’s done to help workers,” arguing that Mr Trump has not come through with an infrastructure programme and has overturned regulations that “will hurt us on the job”.

AFL-CIO president Richard Trumka (AP Photo/Alex Brandon)

Asked about the low unemployment rate and economic growth, Mr Trumka said: “Those are good, but wages have been down since the first of the year. Gas prices have been up since the first of the year. So, overall, workers aren’t doing as well.”

Mr Trump tweeted: “Our country is doing better than ever before with unemployment setting record lows.”